I read the abstract of that paper, skimmed the rest. The second and third parts of it offer a meta-analysis of studies that tend to show that regular exercise tends to keep people healthier. Doesn’t seem like a very controversial finding, or a very helpful one.
The first part of the paper, in my opinion, suffers from the defect that absence of evidence is not evidence of absence. Their review of the literature fails to find evidence that (over-)exertion temporarily makes an athlete susceptible to infection or other illness. The experience and anecdotes of athletes and coaches generally doesn’t show up in scientific literature.
And they state the wrong, opposite conclusion from at least one of the papers they cite:
- From the linked Campbell & Turner paper: “Contrary to the aforementioned reports that exercise heightens infection incidence, it is often overlooked that other studies indicate that exercise participation may in fact reduce the incidence of infections.”
- From one of the papers they cite: “We conclude that elite endurance athletes can achieve high training volumes only if they also experience few sick-days. […] The less sick you are the more you can train.” (Mårtensson 2014)
For training guidance, I’ll listen more closely to coaches than to academics.
“Strong people are harder to kill than weak people, and more useful in general.” —Mark Rippetoe
(Not sure what happened to my reply – if there are duplicate posts, please ignore…)